Catalytic cracking apparatus

ABSTRACT

A catalytic cracking apparatus comprises a catalyst lift pot having a first diameter, a riser-reactor having a mouth connected to the lift pot and defining a second diameter which is smaller than the first diameter, and a plug member which axially extends into the lift pot from the lower end thereof. The riser-reactor and plug member are situated so that fluid flowing through the lift pot before flowing into the riser-reactor flows radially inward across an upper end surface of the plug member. The apparatus further comprises a device for introducing a fluidizable catalyst through a sidewall of the lift pot, and a device for releasing liquid oil feedstock and atomizing fluid into the lift pot from the upper end surface of the plug member.

BACKGROUND OF THE INVENTION

This application is a continuation of application Ser. No. 541,933,filed Oct. 14, 1983, now abandoned.

In one aspect, the invention relates to a catalytic cracking unit. Inanother aspect the invention relates to a catalytic cracking process.

Excessive steam use in a catalytic cracking unit is undesirable becauseit can deactivate the catalyst. The problem becomes more apparent asheavier feedstocks are charged to catalytic cracking units becauseadditional steam is usually added to disperse the oil feedstock in thefluidized cracking catalyst. Special consideration must thus be given tothe design of the mixing chamber for catalysts and oil where heavy feedsare to be processed.

OBJECTS OF THE INVENTION

It is an object of this invention to provide an improved mixing zone forcatalyst and feedstock in a catalytic cracking unit.

It is a further object of this invention to provide a method foradmixing hot cracking catalyst particles and liquid oil feedstock in acatalytic cracking unit.

It is a further object of this invention to provide an apparatus andmethod for cracking an oil feedstock in which usage of atomizing andfluidizing gas is an independent process variable.

STATEMENT OF THE INVENTION

In accordance with certain aspects of the invention, the lower end of ariser-reactor is connected to the upper end of a catalyst lift pot. Theinside of the lift pot defines a first diameter. The mouth of the riserreactor, where it connects to the upper end of the lift pot, defines asecond diameter which is smaller than the diameter of the lift pot. Aplug member extends axially into the lift pot from its lower end. Theplug member is generally rotationally symetric above its longitudinalaxis and has an upper end surface which faces the mouth of the riserreactor. A means is associated with the upper end surface of the plugmember for releasing a liquid oil feedstock and an atomizing fluid intothe lift pot from the upper end surface of the plug member. Theapparatus further comprises a means for introducing a fluidizablecatalyst into the catalyst lift pot between the plug member and theinterior surface of the lift pot.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates certain features of one type ofcatalytic cracking unit embodying certain features of the presentinvention.

FIG. 2 schematically illustrates in greater detail a portion of thedevice shown in FIG. 1.

FIG. 3 is a cross-sectional view of the apparatus shown in FIG. 2 whenviewed along lines 3--3.

FIG. 4 is a side view of a portion of the apparatus shown in FIG. 3 witha portion broken away to show internal details.

FIG. 5 is a cross-sectional view of a portion of the device shown inFIG. 4 which has been enlarged for detail.

FIG. 6 is a cross-sectional view of the device shown in FIG. 5 as itwould appear when viewed along lines 6--6.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, one type of fluid catalytic cracking unit(FCCU) 2 comprises a riser-reactor 4, a regenerator 6, acatalyst/product separation zone 8 which usually contains severalcyclone separators, and a stripping section or zone 10 in which gas,usually steam such as introduced from lines 12 and 13, strips entrainedhydrocarbon from the coked catalyst. Overhead product from theseparation zone 8 is conveyed via line 14 to a separation zone 16including a main fractionator 17. The product can be separated, forexample, as follows. Light hydrocarbons uncondensed in condenser 21which can be withdrawn from the zone 16 by the line 18. Gasoline rangeliquid accumulated in accumulator 23 can be withdrawn by the line 20 orrefluxed via line 27. Distillates such as light cycle oils can bewithdrawn by the line 22 from stripper 29 after being stripped withsteam introduced via line 31. The overhead of light hydrocarbons 19 fromthe stripper which can be recycled to column 17. Bottoms which can bewithdrawn by line 24 or recycled to the riser by line 25, as desired.

After being stripped in the zone 10, the cracking catalyst is conveyedfrom the zone 10 to the regenerator 6 by line or standpipe 28 for cokeburnoff. In the regenerator 6, molecular oxygen containing gas isintroduced by a line 30 which is connected to a source ofoxygen-containing gas, usually air. Coke deposits are burned from thecatalyst in the regenerator 6 forming an effluent gas which is separatedfrom the catalyst in a plurality of cyclone separators 34. These fluegases are withdrawn from the regenerator 6 by the line 36. Coil 33 inthe regenerator 6 is used to convert boiler feed water introduced vialine 31 to high pressure steam which is withdrawn via line 35. Hotregenerated catalyst passes from the regenerator 6 to a lift pot 37 atthe lower end of the riser-reactor 4 by line 38, which provides a sourceof hot, low carbon containing cracking catalyst particles for theriser-reactor 4.

The catalyst flow rate through the cracking unit is controlled by valves39 which are positioned in the line 38, preferably in a vertical portionthereof.

In the lift pot 37, catalyst from the line 38 is fluidized with afluidizing gas, usually steam, which is introduced into the lift pot 37and/or lower portion of line 38 by lines 41 and/or 43. The oil feedstockis introduced into the lift pot 37 via a nozzle assembly 42 whichpreferably emits an oil spray axially into the riser-reactor 4 at thelower end thereof. A line 44 connects the nozzle assembly 42 with asource of oil feedstock such as a gas oil feed line 45 and the recycleline 25.

Atomizing gas such as steam can be added to the nozzle assembly 42 bylines 46 and/or 47 (see FIG. 2) which connects the nozzle assembly to asteam source.

The operating conditions for the riser-reactor 4 and regenerator 6 canbe conventional. Usually, the temperature in the riser-reactor 4 will bein the range of from about 850° to about 1050° F. preferably in therange of 925° to 1025° F. for heavy oils. The oil is usually admixedwith steam at a weight ratio of oil to steam in the range of from about6:1 to about 25:1. A catalyst:oil weight ratio employed in theriser-reactor 4 is generally in the range of from about 2:1 to about20:1, usually between about 2:1 and about 15:1, preferably between about3:1 to about 10:1. Pressure in the riser-reactor 4 is usually betweenabout 15 and about 60 psia (pounds per square inch absolute), preferablyless than about 25 psia for heavy oils. The cracking catalyst particlesgenerally have a size of the range of from about 20 to about 200microns, usually between about 40 and 80 microns, preferably principallyabout 60 microns. Flow velocity upward in the vertical section of theriser-reactor is generally from about 10 to 30 feet per second in thelower portion up to between about 40 and about 120 feet per second inthe upper portions. The contact time between the catalyst and oil in theriser-reactor is generally in the range of from about 0.25 to about 4seconds, usually from 1 to about 3 seconds when the oil is injected intothe bottom of the riser. Preferably, contact times for heavy oils areless than 2.5 seconds. The regenerator is operated at a temperaturetypically in the range of from about 1100° to about 1500° F., usuallyfrom about 1150° to 1450° F., and is ordinarily provided with sufficientoxygen containing gas to reduce the coke on the catalyst to a level ofabout 0.5 weight percent or less, preferably less than 0.1 weightpercent.

Catalysts suitable for catalytic cracking includes silica-alumina orsilica-magnesia synthetic microspheres or ground gels and variousnatural clay-type or synthetic gel-type catalysts. Most preferably,fluidizable zeolite-containing cracking catalysts are employed.Preferred catalysts can contain from about 2 to about 20 percent basedon total weight of zeolitic material dispersed in a silica-aluminamatrix and have a B.E.T. surface area in the range of 50-500 m² /g and aparticle size chiefly in the range of 40-80 microns.

The lift pot 37 has an upper end 50, a lower end 52 and an interiorsurface 54. Preferably, the interior surface 54 is generally cylindricalin shape. The generally cylindrical interior surface 54 of the lift potpreferably defines a first diameter. The generally cylindrical interiorsurface 54 is centered about a longitudinal axis 56.

The riser-reactor 4 is connected to the upper end 50 of the lift pot 37.The riser-reactor 4 has a lower end 58 attached to the upper end 50 ofthe lift pot. The lower end 58 of the riser-reactor 4 defines a mouthhaving a second diameter where it is connected to the lift pot 37. Thesecond diameter of the mouth of the riser-reactor is less than thediameter across the interior surface 54 of the lift pot. Preferably, theupper end 50 of the lift pot is connected to the lower end or mouth 58of the riser-reactor by an end wall 60, the interior surface of which ispreferably generally annular shaped. The riser-reactor has alongitudinal axis 62 in its lower portions which is preferably coaxialwith the longitudinal axis 56 of the lift pot 37.

The nozzle assembly 42 comprises a plug member 64 and a means 66 forreleasing a liquid oil feedstock into the riser-reactor 4. The plugmember 64 has a longitudinal axis 68 and is generally rotationallysymmetric about its longitudinal axis 68. Preferably, the longitudinalaxis of the plug member 68 is coaxial with the longitudinal axis 62 ofthe lower portions of the riser-reactor 4 and more preferably is alsocoaxial with the longitudinal axis 56 of the lift pot 37. The plugmember 64 extends into the lift pot 37 from the lower end 52 of the liftpot. A lower end wall 70 of the lift pot 37 connects the generallycylindrical sidewall 54 of the lift pot 37 with a lower end 72 of theplug member 64. At least the interior surface of the end wall 70 ispreferably generally annularly shaped. An upper end surface 74 of theplug member 64 faces the mouth 58 of the riser-reactor 4. Preferably,the upper end surface 74 is generally planar. The plug member itself ispreferably generally frustoconically shaped, converging toward the mouthof the riser-reactor from lower end 72 to upper end 74. Usually, theplug member will converge toward the longitudinal axis 62 of theriser-reactor at a half angle measured from the axis 62 of from near 0°to about 60°, usually from about 50° to about 50°, preferably from about5° to about 20°. Preferably, the upper end surface 74 of the plug member64 has a diameter near that of the mouth of the riser-reactor. Generallyspeaking, the diameter of the upper end surface 74 will be between 0.7and about 1.5 times the diameter of the mouth of the riser-reactor.Providing a plug member with a larger diameter will impart a greaterradially inward velocity component to the cracking catalyst at themixing point with the oil while providing the plug member with an upperend surface having a diameter toward the smaller end of the range willimpart greater axial velocity to the cracking catalyst at the point ofmixing with the oil. More preferably, the diameter of the upper endsurface 74 of the plug member ranges from about 1 to about 1.25 timesthe diameter of the mouth of the riser-reactor.

The apparatus further comprises a means 76 for introducing a fluidizablecatalyst into a catalyst lift chamber 78 defined between the plug member64 and the interior surface 54 of the lift pot 37. Generally speaking,the means 76 will comprise a port 80 which opens into the chamber 78 andis connected to a source of hot catalyst particles. Preferably, the port80 is positioned with respect to the source of hot catalyst particles soas to feed from the source the catalyst particles into the lift pot 37.Preferably, the means 76 includes the line 38 which opens into the liftpot 37 through the generally cylindrical sidewall 54. In one embodiment,the port 80 opens into the chamber 78 in a generally tangentialdirection so as to introduce catalyst particles into the chamber 78 tocause a swirling flow around the longitudinal axis 56 of catalystparticles in the chamber 78.

The flow rate of catalyst particles through the riser-reactor 4 can beinfluenced by manipulating the valve 39, and/or the flow of steamthrough steam lines 41 and 43. Excessive back pressure in the liftchamber 78 can reduce catalyst flow through the line 38. The admissionof steam at several points through the end wall 70 toward the mouth ofthe riser-reactor, such as through three nozzles fed by steam line 41 attimes of high pressure in the chamber 78 can assist catalystcirculation. Line 43 admits "aeration or ebulliating steam to thecatalyst passing through the sloping portion of line 38. As line 38tends more toward vertical, less steam need be admitted through the line43. The slope of the standpipe should exceed the solids angle of slideor repose and care should be taken not to admit excessive steam throughthe line 43 because too much steam can hinder solids flow into thechamber 78. From a functional point of view, steam added via line 43 canbe referred to as incipient fluidization steam while steam added vialine 41 can be termed blast or conveying steam.

The riser-reactor 4 preferably includes a first generally cylindricalportion 82 which has the first diameter and is connected to the mouth 58of the riser-reactor 4. A second generally cylindrical portion 84 of theriser-reactor 4 is spaced apart from the generally cylindrical portion82. The second generally cylindrical portion 84 has a third diameterwhich is larger than the first diameter. A generally frustoconicallyshaped portion 86 of the riser-reactor 4 connects the first generallycylindrical portion 82 with the second generally cylindrical portion 84.The first generally cylindrical portion 82, the frustoconically shapedportion 86 and the second generally cylindrically shaped portion 84 arepreferably coaxially aligned along the axis 62 and vertically oriented.Providing the riser 4 with a portion of restricted cross-sectional area,such as the generally cylindrical portion 82 aids in preventing backmixing. It promotes plug flow. The flow regime established at the lowerportion 82 of the riser seems to prevail all the way up the riser. Thetapered section such as the generally frustoconically shaped portion 86provided just above the vaporization section maintains a high velocityof catalyst and gases. It is recognized that volume of gases increasewith time due to liquid oil droplet vaporization in the riser and thatless riser cross-sectional area is needed at the bottom. Toward the topof the reactor, most of the cracking reaction has occurred so a fullsize riser such as the portion 84 is provided spaced apart from themouth 58. Generally speaking, the diameter of the second generallycylindrical portion of the riser will be in the range of from about 1.1to about 2 times the diameter of the riser at the mouth 58.

The means 66 for releasing a liquid oil feedstock and an atomizing fluidinto the lift pot 37 from the upper end surface 74 of the plug member 64preferably comprises a plurality of bifluid nozzles 88. (See FIG. 3) Thenozzles preferably open into the lift pot 37 from spaced apart positionson the upper end surface 74 of the plug member 64. Generally speaking,from about 3 to about 12 of the bifluid nozzles are preferablycircumferentially spaced around the longitudinal axis 68 of the plugmember 64 and at least one nozzle is positioned on or very near theaxis. The bifluid nozzles 88 are provided with slots 90 for the emissionof a mixture of oil feedstock and atomizing fluid and the slots arepreferably generally radially oriented with respect to the longitudinalaxis 68 of the plug member 64. By circumferentially spacing the nozzlesaround the axis of the plug member, oil and catalyst flow atapproximately a 90° angle at the initial point of mixing. The nozzle onthe axis helps to transport the catalyst into the riser. Where the slots90 are radially oriented, the direction of the slot will beapproximately the same as the direction of catalyst flow by the end ofthe plug member.

If desired, dispersal steam from line 46 can be introduced into themouth 58 of the riser 4 from the upper end surface 74 of the plug member64. The introduction of atomizing gas, such as steam, into the riser 4independently of the oil feed can be advantageous in the cracking ofheavy oils. This can be accomplished by the use of a plurality ofconduits 92 connected to the source of atomizing gas such as the steamline 47 opening into the lift pot 37 from the upper end surface 74 ofthe plug member 64. The conduits 92 can open into the lift pot fromspaced apart positions on the upper end surface 74 of the plug member64, preferably from circumferentially spaced apart positions which canbe arranged in one or more circular arrays centered about thelongitudinal axis 68.

Generally speaking, each of the bifluid nozzles 88 comprises an innertube 94 and an outer tube 96. (See FIG. 4) The inner tube 94 ispreferably coaxially positioned within the outer tube 96. The end 98 ofthe inner tube 96 protrudes past the end 100 of the outer tube 96. Thetubes are positioned in a passage 102 which extends longitudinallythrough the plug member 64. The end 100 of the outer tubular member 96is preferably positioned about flush with the upper end surface 74 ofthe plug member 64. The end 98 of the inner tubular member 94 preferablyprotrudes slightly above the upper end surface 74 of the plug member 64.(See FIG. 5) A wall member 104 connects the end 100 of the outer tube 96to a sidewall 106 of the inner tube 94. The end 98 of the inner tube 94is at least partially closed by a suitable end closure such as cap 108.The slot 90 is cut through the end closure 108 on the inner tubularmember 94. The slot extends partially across the cap 108, preferablyelongated diametrically across with respect to the tubular member 94.The sidewall 106 of the inner tubular member 94 is provided with aplurality of apertures 109 extending through the sidewall 106 andestablishes a plurality of flow paths between the inside of the innertubular member 94 and an annulus 110 which is defined between the innertube 94 and the outer tube 96 adjacent the second end 100 of the outertube 96. For good results, the apertures 109 are preferably generallyradially oriented with respect to a longitudinal axis 112 of the innertubular member 94. To further enhance mixing, a plate baffle 114 can bepositioned in the inner tubular member 94, preferably at right angles tothe longitudinal axis 112 mounted by typical four support rods 115. Adisc baffle coaxially mounted in the inner tubular member 94 ispresently preferred. In use, it is preferred to connect the steam sourceto the annulus 110 between the inner tubular member 94 and the outertubular member 96 and the source of oil feedstock to the inner tubularmember 94.

In accordance with certain other aspects of the invention, an oilfeedstock is introduced into a stream of hot cracking catalystparticles. The feedstock is introduced as the hot cracking catalystparticles are moving radially inwardly from the periphery around the endof a plug. The particles of cracking catalysts are caused to flow aroundthe end of the plug by first being flowed longitudinally through a liftpot in an annular stream with the plug in the center of the annulus andthen in a radially inwardly directed stream past the end of the plug dueto the upper confines of the lift pot. At that point, the oil feedstockis injected to form a reaction mixture and the reaction mixture flowsgenerally longitudinally into the riser-reactor.

Desirably, the riser-reactor is provided with a generally cylindricalvaporization zone, a generally frustoconical expansion zone, and agenerally cylindrical reaction zone sequentially arranged in axialalignment and the reaction mixture flows vertically upward in theriser-reactor through the generally cylindrical zone, the divergingexpansion zone, the generally cylindrical zone and into a disengagementchamber. To provide good mixing of catalyst particles and oil feedstock,it is desirable that the catalyst particles and oil feedstock be movingat approximately right angles to each other at the point at which theoil feedstock is introduced into the stream of hot cracking catalystparticles. Generally the oil feed will be sprayed into the stream of hotcracking catalyst particles in admixture with steam to assist invaporization and dispersal of the feed.

In the disengagement chamber, the cracked oil product is separated fromthe catalyst, and sent to a fractionization zone. The cracking catalyst,which contains coke deposits is passed to a stripping zone, stripped,and then passed by gravity to a regeneration zone for contact with anoxygen-containing gas to form the hot cracking catalyst particles. Thehot cracking catalyst particles then feed into the lift pot from theregeneration zone. Generally speaking, the hot cracking catalystparticles are withdrawn from the regeneration zone through a generallyvertically oriented standpipe and the flow rate is controlled as desiredby one or more slide valves positioned in the standpipe. The catalystthen is passed along a downwardly inclined standpipe for introductioninto the lift pot. Steam can be introduced into the lower portion of thelift pot to fluidize the catalyst. The fluidized catalyst is picked upby the flow of oil in atomizing gas from the end of the plug and drawninto the riser-reactor. Preferably, the oil and steam is emitted intothe riser through a plurality of nozzles, each of which has a slottedoutlet with the slot oriented in the direction of cracking catalystflow.

EXAMPLE

The following table illustrates how the invention might be applied to acommercial cat cracker.

                                      TABLE                                       __________________________________________________________________________             Item               Design                                            __________________________________________________________________________    Charge Oil at 470° F.                                                  (25)  Recycle bottoms       9,300                                                                             BPD                                                 Density               11°                                                                        API                                           (45)  Hydrotreated residuum 47,500                                                                            BPD                                                 Density               20°                                                                        API                                                 Atmos. tower side draw gas oil                                                                      2,500                                                                             BPD                                                 Density               33°                                                                        API                                           Riser Steam Added at 470° F.                                                                       40,000                                                                            lb/hr                                         (41) + (43) + (46)                                                            (13)  Stripping Steam at 470° F.                                                                   500 psig                                                (41) + (43) 366° F. Blast Steam                                                              1,800                                                                             lb/hr                                               (38) Regenerated Catalyst at 1280° F.                                                        45  ton/min                                       (30)  Air for Regeneration                                                          Rate                  960,000                                                                           lb/hr                                         Temperature                 440° F.                                          Pressure              55  psia                                          (6)   Regenerator                                                                   Pressure              48  psia                                          Temperature                 1280° F.                                         Dimeter               49  ft                                                  Length                110 ft                                            (4)   Riser-Reactor (in sections from lift pot)                               (a)   Cylinder 82, length   4   ft                                                  Diameter              40  in. I.D.                                      (b)   Cone 86, length       34  ft. 7 in.                                           Diameter              40  diverging                                                                     to 50 I.D.                                    (c)   Cylinder 84, length   103 ft. 9 in.                                           Diameter              50  in. I.D.                                      (d)   Cone Length           3   ft.                                                 Diameter              50  diverging                                                                     to 54 I.D.                                    (e)   Cylinder length       20  ft. 3 in.                                           Diameter              54  in. I.D.                                      (38)  Regenerated catalyst standpipe                                                                      40  in. I.D.                                      (50)  Lift pot cylinder, diameter                                                                         88  in.                                                 Height                72  in.                                           (74)  Top diameter of nozzle support structure                                                            40  in.                                           (72)  Bottom diameter of nozzle support structure                                                         50  in.                                           (74),(60)                                                                           Annulus throat        14.5                                                                              in. from item                                                                 (74) to (60)                                  (66)  8 Nozzles in frustoconical structure with                                     insulation around nozzles and insulcrete                                      cover. Tips of nozzles exposed                                          (90)  Outer nozzles - center distance to                                                                  7   in.                                                 outer edge of top diameter                                                    center distance to structure center                                                                 13  in.                                           (94)  Inner oil pipe - (in) 4   diverging to                                                                  6 I.D.                                        (96)  Outer steam pipe      8   inches                                        (90)  Slot length 2.6 inches                                                  (109) 1/2 inch diameter holes - 2 rows with                                         16 holes - 9 holes in bottom row and                                          7 holes in top row with staggered holes                                       from row to row                                                         (114) 1/2 inch by 3.1 inch disc impingement                                         baffle supported by at least four                                             1/2 inch diameter (item 115) compression                                      rods welded to inside of weld cap (108)                                 (108) 7 in. outside diameter weld                                                   cap, extra hard face inside and out                                           (Stellite #1) cut 2.6 in. wide slot                                           for full 7-inch length top                                              (106) Longitudinal distance on nozzle                                         (a)      from weld on 6 in. I.D. to first                                                                 1.5 inches                                                 row of holes                                                         (b)      from first row to second row of                                                                  2   inches                                                 holes                                                                (c)      from second row to weld cap end                                                                  1.5 inches                                        (d)      from weld cap end to slot bottom                                                                 1.6 inches                                        (92)  fourteen 1-inch diameter steam                                                nozzles for dispersion                                                  __________________________________________________________________________

What is claimed is:
 1. Apparatus comprising:(a) a catalyst lift pothaving an upper end, a lower end, and a generally cylindrical sidewallhaving an interior surface defining a first diameter; (b) ariser-reactor connected to the upper end of the lift pot, saidriser-reactor having a mouth defining a second diameter where itconnects to the lift pot which is smaller than the lift pot firstdiameter; (c) a plug member extending axially into the lift pot from thelower end of the lift pot, said plug member being generally rotationallysymmetric about its longitudinal axis and having an upper end surfacewhich faces the mouth of the riser-reactor, said lift pot, saidriser-reactor and said plug member being construct and arranged so thatfluid flowing through the lift pot before flowing into the riser-reactorflows radially inward across the upper end surface of the plug member;(d) a means for introducing a fluidizable catalyst through the sidewallof the catalyst lift pot between the plug member and the generallycylindrical interior surface of the lift pot; and (e) a means forreleasing a liquid oil feedstock and an atomizing fluid into the liftpot from the upper end surface of the plug member, wherein the means forreleasing liquid oil feedstock and atomizing fluid comprises at leastone bifluid nozzle opening into the lift pot on the upper end surface ofthe plug member, wherein said at least one nozzle comprises an outertube, having an end, and a coaxially positioned inner tube, having anend and a side wall, defining an annulus between the inner tube andouter tube, the end of the outer tube being connected to the outside ofthe inner tube by a wall, the end of the inner tube protruding past theend of the outer tube and having a cap affixed thereto with a slotextending at least partially across it, the sidewall of the inner tubehaving a plurality of apertures connecting the inside of the inner tubeand the annulus between the inner tube and the outer tube, and a platebaffle mounted inside of the inner tube and extending partiallythereacross.
 2. Apparatus as in claim 1 wherein the means forintroducing fluidizable catalyst into the catalyst lift pot comprises atubular member opening into the lift pot through the generallycylindrical sidewall positioned to feed catalyst particles into the liftpot.
 3. Apparatus as in claim 2 wherein the plug member isfrustoconically shaped and tapers toward the riser-reactor and the upperend surface of the plug has about the same diameter as the mouth of theriser-reactor.
 4. Apparatus as in claim 3 wherein the riser-reactorincludes a first generally cylindrical portion having the seconddiameter connected to the lift pot, a second generally cylindricalportion having a third diameter which is larger than the seconddiameter, and a generally frustoconically shaped portion which connectsthe first generally cylindrical portion with the second generallycylindrical portion, said first generally cylindrical portion, thefrustoconically shaped portion and the second generally cylindricallyshaped portion being coaxially aligned and vertically oriented. 5.Apparatus as in claim 4 further comprising a disengagement chamber at anupper end of the riser-reactor and a regenerator, connected to thedisengagement chamber, which is positioned to gravity feed from thedisengagement chamber, and the tubular member which opens through thegenerally cylindrical sidewall of the lift pot is connected to theregenerator.
 6. Apparatus as in claim 5 wherein the at least one bifluidnozzle comprises a plurality of bifluid nozzles.
 7. Apparatus as inclaim 6 wherein said plurality of nozzles includes 3 to about 12 nozzlescircumferentially spaced apart around the center of the upper endsurface of the plug member with the slots radially oriented with respectto the center and at least one of said 3 to about 12 nozzles ispositioned on or near the center of the upper end surface of the plugmember.
 8. Apparatus as in claim 7 further comprising a source of steamconnected to the annulus between the inner tube and the outer tube and asource of oil feedstock connected to the inner tube.
 9. Apparatus as inclaim 8 further comprising a plurality of conduits connected to thesteam source opening into the lift pot from the upper end surface andthe plug member independently from the bifluid nozzles.